A system is disclosed in U.S. Pat. No. 4,322,080 entitled Image Projecting Amusement Device, issued to H. Pennington, wherein the image of an obstacle course and moving target are independently projected on a screen. The moving target image is projected by a player controlled assembly in order to superpose the image of an obstacle course projected by a stationary projector. Optical means are provided for the detection of the overlap of the target and obstacles.
The system described by Pennington achieves obstacle detection by observing the intensity of light reflected from the screen along an optical axis which intercepts the image of the projected target at the screen. The target projector and optical receiver are co-mounted in a fixed relationship on a player controlled pointing assembly so that their respective optical axes intersect at the screen location of the projected target image. Variations in light intensity are detected by the receiver if images of obstacles are superposed by the player controlled target image (the target has "contacted" an obstacle). Because "contact" of a target with an obstacle is sensed by detecting variation in light intensity the projection must occur on a flat, uniform reflectivity surface. This system operates at fixed range and confines the area of play to the screen region.
A markmanship system which provides for the coprojection of visible and infrared light is disclosed by Pardes in U.S. Pat. No. 4,349,337. The system describes a projector for the coprojection of a visible and infrared image which are coincident on a target screen. A pair of infrared detectors are mounted on a separate device simulating a weapon. When this aiming device is pointed at the projected target image a simulated hit is detected. One of the infrared detectors is boresighted with the pointing direction of the aiming device to detect the infrared target image that is present at the location of the visible target image. The other detector is mounted just off this axis and receives light from the scene adjacent to the target image so as to provide a background light reference level. As such the system makes use of unmodulated infrared light in much the same way as the invention to Pennington uses visible light, to detect changes in received light intensity when the image to be detected moves into the receiver field-of-view. The system disclosed by Pardes operates at fixed range subject to the requirement of a uniform projection screen as well.
An earlier patent issued to Pardes, U.S. Pat. No. 4,170,077, describes a markmanship system in which the target projector includes coprojection of visible and modulated infrared light with a receiver which detects the presence of modulated infrared light within its field-of-view. This modulation is achieved by mechanical motion of a grid structure which limits the modulation rate.
The Panosh Group Inc. of Cherry Hill, N.J. recently introduced a toy called "Laser Combat" which comprises a gun and moving reflective target. The gun projects light from an electrically modulated incandescent bulb along a first optical axis and receives retroreflected light from the target along an axis adjacent and parallel to the first. The limited modulation rate requires that the gun dwell on the target at least a tenth of a second for reliable detection of return light.
A game device disclosed in U.S. Pat. No. 4,799,687 entitled Projected Image Tag Game issued to Davis et al comprises an optical transceiver which transmits both visible and infrared light. The function of a given device is to detect the superposition of images projected on arbitrary surfaces by the given device and other such devices. Within a transceiver the source of modulated infrared light and the means for its detection are collocated and are in fact the same device, a light emitting diode which is functionally time division multiplexed. The use of the light emitting diode as a detector significantly limits the range of the transceiver.